Water-Dilutable Stone Impact Protection Paint and Compensation Paint, Their Use and Process For Their Production

ABSTRACT

This invention relates to a method of coating a motor vehicle body including (i) applying as a first layer an electro-dip primer coat; (ii) mixing a water dilutable compensation paint comprising 40 to 80 wt. % binders and a commercial base coat to obtain a mixture, and applying the mixture as a second primer surface layer on said primer coat wherein the primer surface layer applied has a thickness of from 10 to 20 μm; (iii) applying a third layer consisting of a water soluble base coat; and (iv) applying a covering layer of clear coat.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.10/202,382, filed on Jul. 24, 2002, which in turn claims priority toU.S. Ser. No. 08/596,321 filed on Mar. 22, 1996, PCT ApplicationPCT/DE95/00767 filed on Jun. 19, 1995, German Application 19504947.0filed on Feb. 15, 1995, German Application 4421172.4, filed on Jun. 20,1994. The contents of these prior applications are hereby incorporatedby reference in their entireties.

FIELD OF INVENTION

The invention relates to the creation of a water-dilutable stone chipprotection paint and compensation paint, to their use and to processesfor producing the same, especially in the motorcar industry.

BACKGROUND

A basical problem in the lacquering of surfaces, in particular ofmotorcar bodies, is the stone chip resistance of the overall lacquering.The stone impact resistance of conventional paints substantially dependson the primer surfacer layer located on the electrocoat layer and havinga thickness of about 30 to 40 μm which, on the one hand, equalizes therough surface of the crude up minor surface inequalities and mainlyoffers protection motorcar shell to allow subsequent coating with acovering lacquer, fills against mechanical attacks (stone chipprotection function).

A conventional motorcar lacquer coating according to the so-called “basecoat/clear coat process” consists, for example, of a total of fourlayers. These four layers are applied one after the other in separatelacquering devices. The first layer, directly located on the car sheetmetal, is the electrocoat layer which is applied byelectro-dipcoating—mainly cathodic dipcoating (CDC)—for protectionagainst corrosion. The nature of the electro-dipcoating prevents theformation of overspray.

The second layer, located on the electrocoat layer and having a layerthickness of about 30 to 40 μm is the so-called primar surfacer layerwhich, on the one hand, equalizes the rough surface of the crudemotorcar shell to allow subsequent coating with a covering lacquer,levels minor surface inequalities and mainly offers protection againstmechanical attacks (stone chip protection function). This layer issubstantially produced by electrostatic application of a baking enamel,for example, with electrostatic high rotation bell, followed by bakingat temperatures of above 160° C.

The third, layer located on the primar surfacer layer, is the base coatlayer which imparts to the motorcar body the desired color by virtue ofadequate pigments. The water soluble base coat is applied byconventional spray methods.

The fourth and uppermost layer, located on the base coat layer, is theclear coat layer which, analogous to the base coat layer, is applied byconventional spray methods and, on the one hand, imparts the desiredlustre and, on the other hand, protects the base coat againstenvironmental factors (UV radiation, salt water etc.).

SUMMARY

The object of the invention is to create a stone chip protection paintwhich meets the requirements of the tests prescribed by the motorcarindustry and, at the same time, takes over the function of theconventional primar surfacer or the function of the conventional and theconventional base coat layer.

This problem is solved by the present invention by providing awater-dilutable stone chip protection paint, containing from 20 to 60%by weight binders and from 2 to 10% by weight pigments, and by awater-dilutable compensation paint, containing from 40 to 80% by weightbinders. The compensation paint may additionally contain up to 20% byweight pigments.

DETAILED DESCRIPTION

Pigments, as defined by the present invention, include inorganic ororganic multicoloured or achromatic colorants that are practicallyinsoluble in the medium in which they are applied, such as described,for example, in “Glasurit-Handbuch Lacke und Farben”, 11th edition,published by Curt R. Vincentz, Hannover 1984, p. 97-108, i.e. carbonblack titanium dioxide, effect pigments, such as aluminum bronzes, micapigments and the like.

A binder as defined here and in the following includes substances whichbond together similar or different kinds of substances, in particularthe non-volatile component of a lacquer without pigment and filler, butincluding plasticizers, drying agents and other non-volatile additives,preferably the water compatible film-forming resins, such as polyester,polyurethane and acrylate resins and the like, as described, forexample, in “Glasurit-Handbuch Lacke und Farben”, loc. cit. p. 19-96 orin H. Wagner, H. F. Sarx “Lackkunstharz e”, Carl Hanser Verlag Munich1972.

In a further embodiment of the invention, the ratio of binders topigments in the water-dilutable stone chip protection paint is between5:1 and 12:1 or between 10:1 and 15:1 in the case of the water-dilutablecompensation paint.

Inasmuch as the water-dilutable stone chip protection paint or thecompensation paint contains pigments, the latter can be an effectpigment, in particular an aluminium bronze.

In a preferred embodiment of the invention, the binder of the stone chipprotection paint or the compensation paint is a water compatible blockedisocyanate, a polyurethane resin, a polyester resin and/or melamineresin.

In a further embodiment of the present invention, this polyester resinhas an average molecular weight of from 5,000 to 10,000, exhibits anadequate number of carboxyl groups which after neutralisation with basesimpart to the polyester resin sufficient water-dilutable properties; andcontains functional groups, in particular hydroxyl groups by virtue ofwhich the polyester resin is made cross-linkable.

The polyester resin can have a OH number of from 20 to 80, in particularfrom 30 to 60 and an acid number between 10 and 50, in particular from15 to 35.

Its glass transition temperature (Tg) may be between −20 and +30.

In a further embodiment of the invention, the polyester is in particulara polycondensation product of a diol and a dicarboxylic acid in thepresence of a component containing more than 2 functional groups.

The diol is selected from the group consisting of 1,6-hexanediol,neopentyl glycol, 1,4-dimethylolcyclohexane, hydroxypivalic acidneopentyl glycol ester (HPN), perhydrogenated bisphenol A,trimethylolpropane and trimethylolpropane monoallyl ether.

The dicarboxylic acid is selected from the group consisting of adipicacid, phthalic acid, isophthalic acid, hexahydrophthalic acid,tetrahydrophthalic acid or their possible anhydrides, in particular fromthe group of dimeric fatty acids.

The component containing more than 2 functional groups may be a triol, atricarboxylic acid, a monohydroxydicarboxylic acid, in particular adihydroxymonocarboxylic acid, preferably trimellithic acid,trimethylolpropane and dimethylolpropionic acid.

The best properties can be achieved with binders exhibiting elastomericcharacteristics after baking. These can be specific polyurethanes inwhich, due to their segmented structure, a specific sequence of soft andhard segments is observed. Preferred binders are soft polyester resinshaving a high molecular weight and a high hydroxy-functionality,obtained by polycondensation of dimeric fatty acids and polyalcohols,preferably diols, their crosslinked sites being produced bytrifunctional (hydroxy)carboxylic acids. These polyester resins are alsoused with blocked polyisocyanates or melamine resins as cross-linkingagents.

Furthermore, the water-dilutable stone impact-protection paint orcompensation paint can additionally contain organic solvents andadditives.

The term solvent as used hereinafter includes those organic substanceswhich can dissolve other substances in a physical manner, such as, e.g.,lower alcohols, glycol ether, lower ketones, in particular organicsolvents which are substantially miscible with water, such as butanol,isopropanol, methylethyl ketone and many others, such as described forexample, in “Glasurit-Handbuch Lacke und Farben”, loc. cit. pages117-138.

Additives are defined as substances that are added in small amounts toother substances, in particular liquid substances, to change theirproperties in a desired manner or to facilitate their processing.Additives include gloss products, wetting agents, drying agentssedimentation inhibitors, antifloating agents, film-inhibiting agents,leveling agents, release agents, lubricants as well as UV absorbers,biocides, plasticizers, antistats, stabilizers, antioxidants,antiozonants, fillers, viscosity control agents, aging inhibitors,detergents, dispersing agents, defoamers, setting accelerators,solidification retarders or drying agents, as described, e.g., in“Glasurit-Handbuch Lacke und Farben”, loc. cit. p. 113-117.

The invention also relates to the use of a water-dilutable stone chipprotection paint for coating motorcar bodies having an electro-dipprimer coat, a second so-called primar surfacer layer, a third layercomprising a water-soluble base coat and a covering layer of clear coat,the primar surfacer layer being replaced by a stone chip protectionlayer consisting of the stone chip protection paint and having athickness of from 10 to 20 μm.

In a further embodiment of the present invention, the water-dilutablestone chip protection paint is used for coating motorcar bodies havingan electro-dip primer coat, a stone chip protection layer consisting ofthe stone chip protection paint having a thickness of from 10 to 20 μmand a covering layer of clear coat.

The water-dilutable compensation paint of the present invention is usedin mixture with a commercial base coat for coating motorcar bodieshaving an electro-dip primer coat, a second so-called primar surfacerlayer, a third layer consisting of a water-soluble base coat and acovering layer of clear coat, the primar surfacer layer being replacedby a mixture of water-dilutable compensation paint and commercial basecoat having a thickness of from 10 to 20 μm.

A commercial base coat refers to a base coat that is commerciallyavailable from manufacturers/vendors, such as Bollig & Kemper, DuPont,ICI, BASF Coatings, and PPG. It is well known in the art that a basecoat contains as essential components one or more pigments, one or morebinders, and one or more solvents. See EP 0502934B1. Well-knowncommercial base coats include, but are not limited to, Heliotherm Hydro(Bollig & Kemper), Metallucid (Bollig & Kemper), Standox (formerlyHerberts, now DuPont), R-M (BASF Coatings), and ONYX (BASF Coatings).

According to another embodiment of the invention, the water-dilutablecompensation paint is used in mixture with a commercial base coat forcoating motorcar bodies having an electro-dip primer coat, a layercomprising the mixture of water-dilutable compensation paint andcommercial base coat having a thickness of from 10 to 20 μm and acovering layer of clear coat.

Thus, the compensation paint serves for conditioning the base coat, i.e.it imparts to a conventional base coat stone chip protection and primarsurfacer properties so that the base coat either replaces only theprimar surfacer layer (four layer-structure) or the primar surfacerlayer and the base coat layer simultaneously (three layer-structure).

This conditioning adapts in particular the adhesion of the stone chipprotection layer in such a manner that if a strong mechanical load froman outward source acts on the overall lacquering, which upon using athree layer-coating (i.e. without primar surfacer layer) without thelayer of the present invention, would lead to a chipping off of theelectrocoat layer, the adherence to the electrocoat layer is controlledto such an extent that, on the one hand, the stone chip protection layeris released from the electrocoat layer, but does not pull the latterfrom the motorcar sheet metal and, on the other hand, the chipping offsare as little as possible. The latter can be achieved by additives whichspecifically increase the rebound resilience of the stone chipprotection paint. Rebound resistance as used herein means the propertyby means of which a mechanical impulse (stone impact) is counterbalancedby an elastic deformation. A damage of the material is inhibitedthereby.

There are different methods of testing the property of predeterminedstability of the pertinent layer, namely of said stone impact protectionpaint or of a base coat conditioned by said compensation paint, saidmethods being adapted to the specific field of application, however, allof them aim at reproducing the mechanical action as exactly as possible.There are, for example, prescribed tests in the motorcar industry whichtry to simulate the stone impact by the impact of a shot (Mercedes-BenzAG, lacquer testing apparatus with shot testing apparatus attemperatures of −20 to +50° C., a shot diameter of from 2 to 4 mm and ashot speed of from 50 to 300 km/h) or a chisel-like testing device (TestVDA 621-428 of BMW-AG) on the finished lacquered surface at exactlydefined temperatures (room temperature and −20° C.) and further exactlydefined parameters.

In a particularly preferred embodiment of the invention, thewater-dilutable stone impact protection paint contains overspray fromwater-soluble base coats, in particular from spraybooth waste water.

An overspray is the excess of lacquer which during the application ofthe lacquer by spray painting techniques does not hit the article beinglacquered but misses the target and is discharged together with theexhaust air from the lacquering zone in order to be transferred, forexample in a wet wash out step, to the wash out water of thespraybooths—referred to hereinafter as booth waste water—to wash out thelacquer components present in the overspray.

A big problem generally encountered in lacquering processes is the wastematerial, in particular paint sludges. Paint sludges are usuallyproduced when the substantially water-insoluble lacquer components areremoved from the booth waste water by coagulation to allow the boothwaste water, recovered after sedimentation or separation of the paintsludge, to be recycled for reasons of environmental protection.

In view of the high costs of waste disposal, the lacquer manufacturingand the lacquer processing industries are increasingly interested inapplying new methods to avoid this kind of waste. To this end, there arebasically two possibilities. On the one hand, one is trying topractically inhibit the formation of an overspray right from thebeginning by applying specific and more sophisticated lacqueringmethods. The latter include flow coating, casting, dipcoating, rollcoating, coil coating, electro-dipcoating or the like. On the otherhand, one is trying to recycle the overspray which is necessarily alwaysformed, for example, when using spray painting techniques. At present,the degree of coating efficiency of this spraying method (air, airlessor air mix atomization etc.) is from 20 to 80%, i.e. only from 20 to 80%of the sprayed lacquer hit the surface of the article being lacquered,the rest accrues as overspray.

A conventional water-soluble base coat usually consists of

from 5 to 15% by weight pigments,from 10 to 20% by weight binders0 to 20% by weight organic solvents0 to 5% by weight additives40 to 85% by weight water.

A particularly serious problem is the recycling of base coat oversprays.Since, for logistic reasons, the motorcar bodies in a factory are notsprayed serially with the different colors (i.e. not only black onmondays, only white on tuesdays and only red bodies on wednesdays etc.)but several color shades within one hour, one always obtains a variableamount of water-soluble base coat overspray of different colors in thebooth waste water. Therefore, the booth waste water has an unsightlyshot color from sludgy brown to dirty gray. This excludes the return ofthis component to the base coat being coated, as proposed in DE-OS 42 13671.

To date, in all motorcar body lacquering plants, theoverspray-containing booth waste waters are converted into a lacquersludge by coagulating agents. In former times, this lacquer sludge wastransported to a waste dump, which is now forbidden by law Therefore,nowadays this coagulate or paint sludge, which still contains about 50%by weight water, is reprocessed, after removal of the main amount ofwater, drying in rotating tubular kilns and grinding to form granulatesor powder, and is reutilized for other purposes. This means in the caseof the granulates, that they are disposed of by the so-called “thermalrecovery”, i.e. incineration of special waste. The energy recoveredthereby does neither compensate the loss of material nor the expenditureof method and capital.

The recovery of the booth waste water-overspray in the sense of arecycling to the spraying process, i.e. a recovery on a higher level, isonly possible in the processing of water thinnable lacquers. Waterthinnable lacquers are those systems which contain, beside theconventional lacquer components, water-dispersible binders and whichhave water as main solvent. When using water thinnable lacquers in spraycoating techniques, one has the possibility of precipitating theoverspray in the booth waste water in such a manner that coagulationdoes not take place. Thus, the booth waste water becomes a very dilutedwater thinnable lacquer which can be depleted from excess water bysuitable methods and be reutilized as lacquer. Thus, DE-OS 42 13 671describes a process for recovering the overspray from aqueous coatingcompositions during spray coating in water dripping spraybooths by meansof ultrafiltration which allows to concentrate the enriched booth wastewater (retentate) to a solids content of up to 35% by weight. DE-OS 4207 425 describes a process for recovering the lacquer overspray ofaqueous lacquers during spray coating by ultrafiltration and sebsequentelectrophoresis. Further processes for recovering water thinnablelacquer oversprays are described in DE-OS 34 28 300, CH-OS 1656/59,DE-OS 41 33 130 and DE-OS 42 02 539.

It has also been contemplated to recycle the booth waste water until awater thinnable lacquer concentration is obtained in said booth wastewater which permits the direct use of the latter as thinnable lacquer.JP-PS 49 51 324 teaches to increase the concentration of lacquer in thelacquer-containing precipitate by removal of water from the entire boothwaste water to such an extent that this precipitate can be reutilizedfor color spray painting. However, practical tests showed that aconcentration of thinnable lacquers in booth waste water to a solidsconcentration of more than 2% by weight results in that the overspray isno longer completely washed out and the discharged exhaust air containsmore overspray than is prescribed by the law (technical instructions onair quality control). The solids concentration refers to the overallamount of non-volatile lacquer components, such as pigments, binders,additives etc., expressed as weight percent, based on the total contentof all lacquer components.

DE-OS 42 13 671 and 41 33 130 teach methods of recovering the overspraysof aqueous coating compositions during spray coating in spray boothsaccording to which part of the liquid circulating in the ultrafiltrationcycle is used as aqueous coating composition for spray coating. Thiscirculating liquid is alway added to the same spraying composition fromwhich overspray it is obtained.

The overspray comprising aqueous base lacquers for producing a stoneimpact protection layer which dries at from 50 to 90° C. is usedaccording to the invention between the electrocoat layer and the baselacquer layer.

For the purposes of the invention, the overspray can be recovered by anyconventional method. Its accumulation can be effected, for example,according to the lacquer recovery methods described in I-Lack 61 (1993),p. 425-428 (washer device, recovery wall, recovery belt, Relaslamella-recovery system). The overspray is preferably recovered in acondition allowing its use according to the invention by means of anyprior art wet wash out method. This wet wash out results in anaccumulation of the overspray in the booth waste water.

With respect to the composition of the individual lacquer components,the overspray in the booth waste water has a different composition fromthe base coat since, for example, the evaporation of the volatileorganic solvents is quicker and, therefore, escape to the atmospheretogether with the exhaust air from the spraybooth.

The booth waste water normally consists of

form 0.1 to 1.5% by weight pigments,from 0.1 to 2.0% by weight binders,from 0 to 2.0% by weight organic solvents,from 0 to 0.5% by weight additives andfrom 94 to 99.8% by weight water.

Booth waste water containing an overspray which consists ofwater-soluble base coats of different colors is preferably used for thepurposes of the invention.

This booth waste water is preferably used in a water-depleted upgradedform in the light of the invention. This upgrading by water depletioncan be effected by any separation procedure familiar to the expert, suchas concentration by vaporization, concentration by boiling in vacuo,freezing out, centrifugation or freeze drying. An upgrading of the boothwaste water is usually conducted by ultrafiltration or a combination ofultrafiltration and electrophoresis (DE-OS 42 97 425).

This upgraded booth waste water has a solids concentration of from 10 to35% by weight. In the upgrading of overspray absorbed in water, changesin respect of the composition of the concentrate because, for example,preferably water-insoluble and high molecular weight components such aspigments and binders are retained by ultrafiltration while the watersoluble and low molecular weight components, such as solvents, melamineresins and neutralizing agents preferably are transferred to thepermeate. The water depletion can also result in a change of theproperties of the paint components, such as color shade and rheology.

The upgraded booth waste water usually consists of

from 2 to 12% by weight pigments,from 4 to 18% by weight binders,from 0 to 5% by weight organic solvents,from 0 to 0.8% by weight additives,from 64 to 94% by weight water.

Thus, by virtue of the production of the stone chip protection paint ofthe present invention, a big problem of the spray coating techniqueaccording to the “base coat/clear coat” method is solved because all ofthe overspray accrued in the spray coating of the base coat layer in thebooth waste water can be utilized. This means that it is no longernecessary to coagulate booth waste water and, consequently, paint sludgeis not obtained when the base coat layer is applied.

In addition, this means that both the base coat overspray as well as theoverspray of the stone chip protection paint recovered therefrom can beunited in one booth waste water.

A basical advantage of using booth waste water for producing stone chipprotection paint is that the booth waste water may also containdifferent color shades of the water-soluble base coats and can,nevertheless, be reutilized as valuable material.

A further particular advantage in replacing the conventional fillerlayer by the stone chip protection layer of the present inventionconsists in that the baking of this primar surfacer layer can bedispensed with. The stone chip protection layer of the present inventiondries at a temperature of between 50 and 90° C. and, consequently,necessitates, for example, only a drying or a predrying with infraredradiation. This means a considerable saving of energy and time.Moreover, it is not necessary to apply the stone chip protection layerof the present invention with the same layer thickness as the primarsurfacer layer; it is enough if said stone chip protection layer has athickness between 10 and 20 μm to possess the same mechanical propertiesas the conventional primar surfacer layer. This also means aconsiderable saving of material.

A further advantage over the prior art is that two instead of threebooth waste water cycles have to be installed. The recycling of theclear coat, e.g. by ultrafiltration, makes it possible to run for thefirst time a motorcar standard lacquering which is completely free ofpaint sludge. When water borne clear coats are used, it is even possibleto run the process with only one booth waste water cycle if the coatingefficiency of the water borne clear coat application is optimized bysuitable methods such that the accrued amounts of overspray do notexceed the demand for the stone chip protection paint of the presentinvention. Besides, the demand for stone chip protection paint can becontrolled by varying the layer thickness, (in particular heightening).

In case the stone chip protection paint, manufactured according to theinvention from the concentrated booth waste water, does not exhibit thedesired protective properties against mechanical load acting on theoverall lacquering from outside, it can be conditioned as specified inthe invention.

This conditioning is effected by adding the components necessary for thedesired properties of the stone chip protection layer. It can also beadvantageous to remove the effect pigments, partly or completely.

The object of this conditioning is, in particular, to adjust theadhesion of the stone impact protection layer in such a manner that if astrong mechanical load acts on the overall lacquering from outside,which without the stone chip protection paint of the invention and theuse of a three-layer lacquering (i.e. without primar surfacer layer)would entail a chipping off of the electrocoat, the adhesion to theelectrocoat layer is adapted in such a manner that, on the one hand, thestone chip protection layer is released from the electrocoat layer butthe latter is not torn off therewith from the motorcar body and, on theother hand, the chipping offs are as small as possible. The latter canbe achieved by additives which increase the rebound resilience of thestone chip protection paint to a predetermined degree. The term reboundresilience stands for the property by means of which a mechanicalimpulse (stone impact) is compensated by an elastic deformation. Adamage of the material is thus inhibited.

The above-mentioned mechanical loads acting on the overall lacqueringfrom outside may involve any kind of mechanical action, such as, forexample, stone impact on motorcar lacquerings, frictional contact orimpact contact between lacquered articles or any kind of objects onlaquered surfaces.

For conditioning the mechanical properties of the stone chip protectionpaint of the present invention, binders, such as a water compatibleblocked isocyanate, a melamine resin, a polyurethane resin or polyesterresin; organic solvents, pigments or additives can be used as suitablecomponents.

These components can be added to the stone chip protection paint aloneor in any combination or also as compensation paint having a solidsconcentration of from 20 to 80% by weight.

This compensation paint contains all or parts of the componentsnecessary for conditioning the desired mechanical properties of thestone impact-protective layer.

Thus, a stone chip protection layer cycle is formed according to theinvention, to which base coat overspray and compensation paint areperiodically added.

Subsequent to the conditioning of the upgraded booth waste water anequilibrium is established after some time within said cycle which canbe maintained by the appropriate amount of compensation paint, which canbe easily determined by the expert.

The particular advantage in the use of the compensation paint resides inthat all components can be added to the stone chip protection paint,adapted to the pertinent base coat system, to the correspondingoverspray or to the booth waste water, and that in a single mixingprocedure directly in the spray coating plant or its directneighbourhood. Therefore, the concentrated booth waste water, which cancontain up to 90% water, must not be transported from the lacquerprocessing plant to another place where it is tested in respect of theproperties required for the stone chip protection layer and, if desired,conditioned by the method of the present invention, but all theseprocedures can be done in the same place where the lacquering isconducted.

The higher the concentration of the compensation paint, the less watermust be removed from the booth waste water.

The process of lacquering motorcar bodies comprises applying anelectro-dipcoat primer (CDC), baking the same, applying the stone chipprotection paint of the present invention, drying the same at 50-90° C.,applying a base lacquer, drying the same at 50-100° C., applying a clearcoat and subsequently jointly baking the three lacquer layers at130-160° C.

The stone chip protection paint of the present invention can be used forlacquering all solid, plane or non-planar smooth or uneven metallicsurfaces which are coated according to the above-specified “basecoat/clear coat process” and which are to be protected againstmechanical load outwardly acting on the overall lacquer, said protectionpaint being located between the electrocoat layer and the base coatlayer. Smooth metallic surfaces, such as occur in the lacquering ofplants, apparatuses, windows, in particular motorcars (cars, trucks,bikes etc.) are mainly involved.

The following examples will illustrate the invention.

EXAMPLES Preparation Example A of a Polyester Resin

In a reactor provided with stirrer, condenser and heater, as well as apacked column, 1187 g 1,6-hexanediol and 1473 g dimeric fatty acid(Pripol 1009 of the UNICHEMA company) are weighed and heated such thatthe head temperature of the column does not exceed 100° C. The maximumesterification temperature amounts to 220° C. When the acid number isbelow 5, cooling to 150° C. is effected and 1499 g admerginic acid (anaddition product of linseed oil fatty acid and maleic anhydride,commercial product of the HARBURGER FETTCHEMIE) are weighed. Heating isagain conducted in such a manner that the head temperature of the columndoes not exceed 100° C. The maximum esterification temperature amountsto 220° C. Cooling is effected at an acid number of 38, followed bydilution with 1658 g Butyl glycol. A polyester having a solids contentof 70% and a hydroxyl number of 57 is recovered.

Preparation Example B of a Polyester Resin

In a reactor provided with stirrer, condenser and heater, as well as apacked column, 598 g dimethylolcyclohexane, 3098 g dimeric fatty acid(pripol 1009 of the UNICHEMA company) and 371 g dimethylolpropionic acidare weighed and heated in such a manner that the head temperature of thecolumn does not exceed 100° C. The maximum esterification temperatureamounts to 220° C. Cooling is effected at an acid number of 30, followedby dilution with 1651 g butyl glycol. A polyester having a solidscontent of 70% and a hydroxyl number of 30 is obtained.

Example 1 Compensation Paint

337 parts of a polyester resin of preparation example A are mixed with ablend of 227 parts of fully desalted water and 12 parts dimethylethanolamine with stirring. 39 parts of the commercial melamine resin LuwipalLR 8852 are added thereto with further stirring. The pH value is 9.06.The viscosity is adjusted by fully desalted water to 130 sec., measuredin DIN 4 (German standard) cup.

Example 2 Compensation Paint

404 parts of the polyester resin of preparation example B are mixed witha blend of 457 parts of totally desalted water and 10 partsdimethylethanol amine with stirring. 47 parts of the commercial melamineresin Luwipal LR 8852 are added thereto with further stirring. The pHvalue is 9.06, The viscosity is adjusted by fully desalted water to 130sec., measured in DIN 4 cup.

Example 3 Compensation Paint

206 parts of the polyester resin of preparation example B are mixed withstirring with a blend of 289 parts totally desalted water and 7.5 partsdimethylethanol amine. 298 parts of the blocked isocyanate Bayhydrol LS2050 of the Bayer AG company Leverkusen are added thereto with furtherstirring. The pH value is adjusted with an aqueous 10%—dimethylethanolamine solution to 8.5. The viscosity is adjusted by fully desalted waterto 130 sec., measured in a DIN 4 cup.

Example 4 Reprocessing of Overspray

A laboratory spray booth having a water capacity of 250 liters wasfilled with fully desalted water. Five different water base coat-colorshades, prepared as described in European patent 502 934, were sprayedwith a flow beaker spraying gun. About 2 to 3 kg of each color shadewere consumed until the solids content of the booth recycling water hasincreased to 1%.

The so-obtained booth water was upgraded to a solids content of 18% byultrafiltration.

Example 5 Stone Chip Protection Paint

2 parts of the commercial melamine resin Cymel 327 are added to 390parts of the retentate of the above-described reprocessing withstirring. 268 parts of the compensation paint of example 1 are added tothis blend and the viscosity is adjusted to 35 sec. by fully desaltedwater.

Example 6 Stone Chip Protection Paint

78 parts of each of the same five water base lacquer-color shades whichwere used to simulate the overspray (as described in example 4) aremixed with stirring. 268 parts of the compensation paint of example 1 isadded thereto, likewise with stirring. After adjusting the pH value tobetween 9.0 and 9.1, the viscosity is adjusted by fully desalted waterto 35 sec.

The stone chip protection paints were sprayed according to conventionalmethods on phosphated sheet steels coated with a commercialelectro-dipcoat. After a flash off time of 3 minutes, drying wasconducted at three different temperatures. One part of the sheets wasdried for 10 minutes at 100° C., the second part for 10 minutes at 130°C. and the third part for 10 minutes at 105° C. The dry layerthicknesses were between 14 and 19 μm. Thereafter, all sheets wereoverpainted in a conventional manner with commercial water base coat and2 components clear coat comprising mainly isocyanate.

Example 7 Base Coat with Integrated Stone Impact Protection Paint

100 parts of a metallic base coat with a silver color shade, prepared asdescribed in European Patent 502 934, were blended with 135 parts of thecompensation paint of example 3 with stirring, and adjusted to aviscosity of 45 sec. (DIN 4).

The so-modified base coat is sprayed on phosphated sheet steels coatedwith a commercial electro-dipcoat and after a flash off time of 5minutes is overpainted with clear coat. The layer thickness of the firstmodified base coat layer was 9 μm and that of the second unmodifiedlayer 7 μm.

All sheets exhibited a good appearance, comparable to conventionalstandards.

The sheets were subjected to a stone impact test, as is common atMercedes Benz AG. To this end, the test sheets were first cooled to −20°C. and were shot with a steel ball having a diameter of 3 mm at a speedof 250 km/h. A penetration up to the sheet should not occur thereby andthe chipping offs should not be greater than 8 mm². All test sheetspassed this test.

1. A method of coating a motor vehicle body comprising: (a) applying asa first layer an electro-dip primer coat; (b) mixing a water dilutablecompensation paint comprising 40 to 80 wt. % binders and a commercialbase coat to obtain a mixture, and applying the mixture as a secondprimer surface layer on said primer coat wherein the primer surfacelayer applied has a thickness of from 10 to 20 μm; (c) applying a thirdlayer consisting of a water soluble base coat; and (d) applying acovering layer of clear coat.
 2. A method of coating a motor vehiclebody comprising: applying as a first layer an electro-dip primer coat,mixing a water dilutable compensation paint comprising 40 to 80 wt. %binders and a commercial base coat to obtain a mixture, and applying asa second layer a layer of thickness from 10 to 20 μm comprising themixture, and then applying a covering layer of clear coat onto thesecond layer.
 3. The method of coating a motor vehicle body of claim 1,wherein the water dilutable compensation paint additionally comprises upto 20 wt. % pigments.
 4. The method of coating a motor vehicle body ofclaim 3, wherein the ratio of binders to pigments is from 10:1 to 15:1.5. The method of coating a motor vehicle body of claim 1, wherein thebinder is a water compatible acrylate resin.
 6. The method of coating amotor vehicle body of claim 1, wherein said binder is a water compatibleblocked isocyanate, a polyurethane, polyester or a melamine resin. 7.The method of coating a motor vehicle body of claim 6, wherein saidbinder is a polyester resin, said polyester resin has an averagemolecular weight of from 5,000 to 10,000, exhibits sufficient carboxylgroups which impart to the polyester resin, after neutralization withbases, sufficient water-dilutable characteristics and containscrosslinkable functional groups.
 8. The method of coating a motorvehicle body of claim 6, wherein said binder is a polyester resin, saidpolyester resin has a OH-number of from 20 to 80 and an acid number offrom 10 to
 50. 9. The method of coating a motor vehicle body of claim 6,wherein said binder is a polyester resin, said polyester resin has aglass transition temperature (Tg) of from −20 to +30° C.
 10. The methodof coating a motor vehicle body of claim 6, wherein the binder is apolyester resin, said polyester is a polycondensation product of a dioland a dicarboxylic acid in the presence of a component containing morethan two functional groups.
 11. The method of coating a motor vehicle ofclaim 10, wherein the diol is selected from the group consisting of1,6-hexandiol, neopentylglycol, 1,4-dimethylolcyclohexane hydroxypivalicneopentyl glycol ester (HPN), perhydrogenated bisphenol A,trimethylolpropane trimethylolpropane monoallyl ether and mixturesthereof.
 12. The method of coating a motor vehicle body of claim 10,wherein the dicarboxylic acid is selected from the group consisting ofadipic acid, phthalic acid, isophthalic acid, hexahydrophthalic acid,tetrahydrophtalic acid or their anhydrides, from the group of a dimericfatty acid and mixtures thereof.
 13. The method of coating a motorvehicle body of claim 10, wherein the component containing more than twofunctional groups is selected from the groups consisting of a triol, atricarboxylic acid, a monohydroxydicarboxylic acid, adihydroxymonocarboxolic acid and mixtures thereof.
 14. The method ofcoating a motor vehicle body of claim 10, wherein said componentcontaining more than two functional groups is selected from the groupconsisting of trimellithic acid, trimethylolpropane, in particulardimethylolpropionic acid and mixtures thereof.
 15. The method of coatinga motor vehicle body of claim 1, wherein the compensation paint furthercomprises organic solvents and additives.
 16. The method of coating amotor vehicle body of claim 2, wherein the water dilutable compensationpaint additionally comprises up to 20 wt. % pigments.
 17. The method ofcoating a motor vehicle body of claim 1, wherein the ratio of binders topigments is from 10:1 to 15:1.
 18. The method of coating a motor vehiclebody of claim 2, wherein the binder is a water compatible acrylateresin.
 19. The method of coating a motor vehicle body of claim 2,wherein said binder is a water compatible blocked isocyanate, apolyurethane, polyester and/or a melamine resin.
 20. The method ofcoating a motor vehicle body of claim 2, wherein the compensation paintfurther comprises organic solvents and additives.
 21. A method ofcoating a motor vehicle body comprising: applying as a first layer anelectro-dip primer coat, mixing a water dilutable compensation paintcomprising 40 to 80 wt. % binders and a base coat to obtain a mixture,and applying onto the first layer the mixture as a second layer ofthickness from 10 to 20 μm, and then applying a covering layer of clearcoat onto the second layer.